Equimoler solulition of HF, HCOOH and HCN at 298 K have the values of Ka as `6.8xx10^(-4), 1.8xx10^(-4)` and `4.8xx10^(-9)` respectively, what will be the order of their acidic strength ?
A. `HFgtHCIgtHCOOH`
B. `HFgtHCOOHgtHCN`
C. `HCIgtHFgtHCOOH`
D. `HCOOHgtHCNgtHF`